The hydroformylation of unsaturated compounds is a well-established process which for many years has been operated on a commercial scale.
In most cases, olefins are used as starting material, but it is known that the hydroformylation of other ethylenically unsaturated compounds such as unsaturated esters and unsaturated alcohols can be successfully performed as well.
However, the presence of substituents in ethylenically unsaturated compounds may cause problems, even if the substituents as such do not interfere with the hydroformylation reaction proper. For example, in the hydroformylation of certain unsaturated alcohols, especially allyl alcohols, isomerization of the starting material occurs as a side-reaction (cf J.Falbe "New Syntheses with Carbon Monoxide", 1980 pp 107 and 108) to form aldehydes, at the expense of the yield of the desired hydroformylation product, viz. hydroxy aldehydes. While the said isomerization is a typical side reaction in hydroformylation processes whereby a cobalt-containing catalyst is used, it also occurs, albeit to a lesser extent, when rhodium-containing hydroformylation catalysts are applied. In fact, rhodium catalyzed processes are known, whereby with the aid of special measures the said isomerization even becomes the predominant reaction (cf EP 293.818).
A process for the hydroformylation of lower olefins (or substituted olefins such as allyl alcohol), whereby it is envisaged to optimize the hydroformylation conditions and to minimize the formation of undesirable by-products, is described in GB 2014138. In this process use is made of a catalyst system, comprising a rhodium complex, a tri-substituted phosphine and a diphosphino alkane wherein 2, 3 or 4 aryl groups are present, linked to the two phosphorus atoms.
According to the examples relating to the hydroformylation of allyl alcohol, a rate of about 1650 (moles of product per gram atom of rhodium and per hour) is achieved, while 6.5% of propionaldehyde (isomerization product) is formed.
Another process for the hydroformylation of unsaturated compounds, including that of allyl alcohol, is disclosed in EP 279018. According to this document, the reaction is carried out in the presence of a catalyst system, comprising rhodium in a chemical complex with one or more ligands of the formula ##STR1## and the y bond are linked to adjacent carbon atoms of the ring structure Ar, the groups Ar may contain up to 4 substituents, R.sub.1 to R.sub.4 are specific hydrocarbyl groups, R.sub.3 and R.sub.4 may additionally be hydrogen and the groups Y are independently selected from the elements N, P, As, Sb and Bi.
According to one of the examples allyl alcohol is converted at a rate of about 2700 (moles of product per gram atom of rhodium and per hour), whereby in addition to the desired hydroformylation products 4.4% of propionaldehyde is formed.
In U.S. Pat. No. 4,668,809, a hydroformylation process is disclosed in which as catalyst a rhodium-containing complex is used, additionally comprising a diarylphosphinoalkyl substituted hetero-organic ligand. The document discloses a large number of compounds that may be used as catalyst ligand and indicates a variety of unsaturated compounds, such as substituted and non-substituted olefinic substances that may be applied as starting material.
However, no working example is included, relating to the hydroformylation of allyl alcohol.
It has now been found that, in the hydroformylation of unsaturated alcohols, the rate is increased and the formation of isomerized by-products is further reduced, by selecting a catalyst system which is based on rhodium in combination with certain ligands, containing both phosphorus and nitrogen.